The goal of this study is to inform decisions about fair and appropriate measurement tools for economic evaluations of mental health services interventions. The relative sensitivity of disease-specific and generic outcome measures for mental health interventions will be assessed. Knowing how these types of measures affect results has direct bearing on the feasibility of including treatments for severe mental illness in rankings used to allocate health care budgets across interventions for different types of health problems. The first aim of this study is to compare the performance of disease-specific and generic quality of life instruments in evaluating outcomes for persons dually diagnosed with severe mental illness (SMI) and substance use disorder. The disease- specific instrument for this study will be the Wisconsin Quality of Life Interview (W-QLI), and the generic instruments will be the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) and the EuroQol EQ-5D. The client group will be a convenience sample of 46 client s drawn from a group of 203 persons in the New Hampshire- Dartmouth Psychiatric Research Center. The purpose of the Dual Diagnosis Study was to compare the effectiveness of the assertive community treatment model to standard case management to persons dully diagnosed with severe mental illness (schizophrenia or bipolar disorder) and substance use disorder. The second aim of this study is to determine if differences exist between societal and client preferences for quality of life outcomes. The societal group will be drawn from a convenience sample of 46 residents from the State of New Hampshire. These comparisons will help clarify the role of perspective in determining the results of an economic evaluation.